1. Field of the Invention
The present invention relates to image processing apparatuses for applying image processing to an image, and also relates to image sensing apparatuses such as digital still cameras and digital video cameras.
2. Description of Related Art
Recent years have seen eager development of technologies for suppressing image blur ascribable to camera shake or subject movement. Some of such technologies achieve blur correction optically, but optical blur correction requires a sensor for detecting shake and a mechanism for optically compensating for it. Incorporation of such a sensor and a mechanism, however, is disadvantageous in terms of cost and compactness. This has led to proposal of various technologies for correcting blur through image processing after shooting.
For example, according to one conventional method, a first image having a high resolution but containing much noise is shot by exposure lasting for a short exposure time and in addition a second image having a low resolution but containing little noise is shot by exposure lasting for a long exposure time. Then, based on the image data of the first and second images, the displacement between the two images is detected; their positions are then so adjusted as to cancel the displacement, and thereafter the first and second images are synthesized to generate a corrected image.
Here, an image region where the differential between the first and second images is large is judged to be an edge region, and there the first image is given a comparatively high synthesis ratio; in contract, an image region where the differential between the first and second images is small is judged to be a non-edge region, and there the second image is given a comparatively high synthesis ratio. This helps generate an image with little blur and little noise.
In edge region judgment based on the differential between a first and a second image, however, not only a true edge but also noise is judged to be an edge. This makes it likely that much of the noise in the first image ends up mixing into the corrected image. This makes important such technologies as reduce mixing of the noise in the first image as much as possible.
Moreover, as a result of the position adjustment mentioned above, as shown in FIG. 24, the position of the entire image region 900 of the first image usually does not completely coincide with the position of the entire image region 901 of the second image, producing a region 902 (the hatched region in FIG. 24) where the two entire image regions 900 and 901 overlap and a region 903 (the dotted region in FIG. 24) where they do not overlap. In this case, from the image data in the overlap region 902 between the first and second images, the image 911 in the overlap region 902 on the corrected image is generated, and from the image data in the non-overlap region 903 on the first image, the image 912 in the non-overlap region 903 on the corrected image is generated; then the generated images 911 and 912 are fitted (joined) together, and thus the angle of view (field of view) of the corrected image is made identical with that of the first image.
Inconveniently, in this case, since the image in the overlap region on the corrected image and the image in the non-overlap region on it are generated by different methods, if no additional processing is performed, the fitting boundary on the corrected image may be visible (the difference in noise level between the overlap and non-overlap regions may be visible).